This invention concerns plastic modular conveyor belts, and is particularly concerned with such conveyor belts of the radius type, that travel around curves as well as straight paths, and with fitting a belt of a certain minimum radius to a particular radius of curvature in a spiral conveyor system or in other radius conveyor travel.
Radius conveyor belts of the type with which this invention is concerned are shown in U.S. Pat. Nos. 4,742,907, 4,901,844, 5,181,601 and 5,573,105. So called spiral conveyor belts, which travel in a helical path as driven by a driving cage or tower, are shown or described in U.S. Pat. Nos. 4,901,844 and 5,069,330.
Spiral conveyors are often fitted with modular plastic radius-type conveyor belts which have a certain minimum radius of is curvature. These belts are used to fit a variety of different radii of driving tower on the spiral systems, and thus are often not matched even approximately to the actual radius of the driving tower, the belt thus not fully collapsing at the inner side of the curve and not assuming its minimum radius as it travels along the driving tower. Typically the driving tower has bars which engage against the ends of module rows on the conveyor belt, and in nearly all cases, the spiral conveyor system is operated in an xe2x80x9coverdrivexe2x80x9d condition whereby the driving tower""s actual speed of rotation is slightly faster than the belt inner edge travel speed. As a result, in the typical situation in which the modular conveyor belt is not assuming its minimum radius in being driven by the driving tower, the ends of module rows tend to bunch together and then jerk as a bar of the driving tower finally overcomes the group of row ends and moves forward beyond them. This causes a vibration or chatter to repeatedly occur at many different points along the inner edge of the belt. This repeated sticking and jumping back of the belt modules causes problems of uneven travel, premature wear and unsteady, unstable transport of the items being conveyed.
The same concern exists on non-spiral conveyor belts involving curving travel, where the belt is guided along the inside of the belt on curves and thus the inner edge must slide along a wear strip or guide at the edge of a belt platform. Again, the belt when on a curve whose radius is larger than the minimum possible radius of curvature of the belt can repeatedly stick and then jump forward because of the excess, unused collapse capability between the modules at the inner edge.
Therefore, it is desirable to substantially match the minimum radius of curvature of a belt to the actual radius of curvature of the system on which it is to travel, whether that system is a spiral conveyor belt system or another belt system wherein the belt travels around lateral curves. This is an object of the invention described below.
By the method of the invention, a radius plastic conveyor belt of the type described above is modified and adjusted so as to custom fit the belt to a specific radius of curvature as may be encountered on a spiral conveyor belt system or simply on a belt having lateral curves in its path of travel. In one preferred embodiment of the method the radius belt is defined as a basic radius conveyor belt with modules that allow a degree of collapse to define a preselected minimum radius of curvature small enough to allow the basic radius conveyor belt to be used on a plurality of conveyor systems having different curve radii. A belt system is selected for which the radius plastic conveyor belt is to be fitted, that belt system having curves which are larger in radius than the preselected minimum radius of curvature of the basic conveyor belt.
The basic radius conveyor belt is then modified by restricting its minimum radius of curvature to a larger radius than the preselected minimum radius, the larger radius substantially matching the actual radius of curvature of the belt system to which the belt is to be applied. This modification does not necessarily involve physically changing a belt; instead, the basic radius conveyor belt can be defined as containing a specific series of modules, but not actually assembled in that way. The modification can be simply by placing different elements in the basic belt as it is actually built, to provide the modified-radius belt. This is the intended meaning of the term modification, herein and in the claims.
Modification of the radius can be accomplished in several different ways. One method is to place at the inner side of the basic radius conveyor belt modules that are restricted to a more limited degree of collapse than the other modules, due to having shorter slotted apertures than the other modules, or other structural limitations to collapsing together. This can be done in every row, alternate rows, or every third row, etc., in regular fashion so as to restrict the ability of the belt to collapse together at the inner side in a way such as to limit the overall minimum radius of curvature of the belt, so that the row ends are substantially fully collapsed and bearing against one another at the inside of the curve, preventing chatter and vibration.
Another method for restricting curvature is to use a uniform array of modules, but to add restricting devices to modules at the inner side of the belt relative to curves. These restricting devices can be shims or stops placed in some of the slotted apertures or in other areas of the belt, such as against a center bar of the belt between adjacent projecting link ends, so as to prevent full collapsing together of the belt modules.
The shims or stops or modified modules with lesser degree of collapse can be located elsewhere than at the inner edge of the belt. For example, they could be located at about the middle of the belt, still being effective to limit collapse at the inner edge but allowing a flexibility or springing action at the inner edge which still can be objectionable if the inner edge is quite distant from the point where the collapse is limited. If modules with shorter slotted apertures are used, the slots preferably are positioned so as to allow full extension, to provide for tension across the full width of the belt in straight travel.
Another alternative is to restrict collapse at the same edge of the module rows by use of snap-on (or otherwise attachable) side plates or product holding devices which can be selected to restrict collapse as desired, to substantially match the desired radius. Product holding devices are often provided for snap-in attachment at or near belt edges, to provide a raised barrier. These can be configured to engage with each other in successive rows (or to engage with the succeeding module itself) to restrict radius as needed.
Thus, the invention in its broadest sense comprises a method for fitting a modular plastic radius conveyor belt as closely as possible to the particular radius of the path of travel of a designated installation, the method including defining a basic radius conveyor belt made up of a basic array of modules permitting radius travel in curves having tightness up to a particular minimum radius R1, then, when a particular installation needing a radius belt is designated, that installation having a radius of curvature R2 which is larger than R1, modifying the basic radius belt by restricting the radius of the modular conveyor belt. This is done by substituting different modules at a series of regularly spaced locations or otherwise hampering by a preselected degree the ability of the belt to travel around curves, such that the minimum possible radius of the modified belt is substantially equal to the radius of curvature in the designated installation. The installation may be a spiral conveyor belt or a belt traveling generally horizontally but through lateral curves, particularly when the belt is guided around the curve at the inside edge of the belt.
It is thus among the objects of the invention to substantially match the minimum radius of curvature of a plastic modular conveyor belt to the actual curves of an installation for which the belt is designated, the method comprising modifying a basic set of modules (whether the basic conveyor belt is actually assembled with such modules or not) to restrict the minimum possible radius of the basic belt and thus to modify the belt to fit a particular curvature, and thereby to prevent or minimize chatter or xe2x80x9cstick and slipxe2x80x9d action at the inner edge of belt curves. These and other objects, advantages and features of the invention will be apparent from the following description of a preferred embodiment, considered along with the accompanying drawings.